Gaseous electric discharge lamp



Jan. 11, 1938. J, cox 2,105,138

' GASEOUS Emcmzc DISCHARGE LAMP I I I Filed Oc-t. 28, 1956 k k N \m ag b 7 I 5 4 I l I I l I I I I I I I I I I j I I 6 I z I I I I 1 I KNx/ENTOR:

JAMES L. @ox

A TTORNE Y.

Patented Jan. 11, 1938 I UNITED STATEE 2,105,138 GASEOIUS mrzc'rarc niscw Application Uctober 28, K936, Serial No. 108,017

2 Claims.

The present invention relates to electric gaseous discharge lamps, and in particularto such ,lamps which comprise a thermionic electrode which is attached to a metal disc used as a sealed closure member for a glass envelope.

An object of the invention is the provision of a refractory insulating coating for the metal disc in order to insure that the disc does not act as an electrode for the discharge.

It is known, for example, that an electric discharge lamp can'be made by enclosing a gaseous atmosphere at the proper pressure in a glass tube, or other envelo whose open-ends are sealed to metal discs, the discs acting as electrodes. Such lamps require a high voltage, of the order of several hundred, for operation, and produce sputtering of the electrodes on the glass, blackening the latter. A thermionic electrode of high electron-emitting power can be attached to the disc, thus reducing the operating voltage and the sputtering. To secure the proper temperature for such an electrode, it may be made in the form of a metal wire, wrapped if desired with another wire of smaller diameter, and

5 coated with a highly electron-emitting material. The larger wire, of course, can be arranged in any convenient geometric shape. If desired, a coated cup or disc of metal can be used instead of the coated wire.

Such an electrode will attain, during operation,

an electron emitting temperature, and thus support the discharge. Its higher emitting qualities,

will insure that, during normal operating conditions the discharge will emanate from it, and not from the metal disc. However, during the man-' ufacture of the lamp, it is necessary to pass a discharge between the electrodes before they are rendered thermionically emissive. During such operation, the discharge tends to, start from the disc, causing sputtering of the metal, with a consequent black deposit on the glass near the metal discs. To prevent this, and to insure that, even during the manufacture of the lamp, the discharge emanates from the thermionic electrode, we have found necessary the use of a refractory insulating material on the inside surface of the metal disc. This coating may be, for example, of alumina. It may be put on as a paste of alumina, and water, then dried out. If desired, the insulating coating may be fused to the metal surface as a sort of glaze. Such a coating prevents the discharge from attacking the end cap during the preliminary operation at the lamp which generally accompanies the manufacturing process, and in addition it may allow the disc to act as a capacity member for starting the discharge, and may facilitate the making of the metal to glass seal during manufacture.

Such an electrode and disc can be used to advantage in any gaseous discharge tube, but particularly in those in which a filling of an inert gas and mercury is used.

The drawing shows a side view of a lamp acl0 cording to the invention.

A vitreous envelope I has the metal discs 2 and 3 sealed to its ends, closing them oil. Electrodes 4 and 5, attached to the discs may be of the thermionic type, if desired. They are pref- 1 erably, but not necessarily, of the wire-wound oxide-coated type. They may be attached to the metal discs by welding, or some similar process. Welding generally weakens the disc, so I prefer to support the electrode from a wire 8, 9 2o wrapped in a circular groove I, ll formed on the disc. To permit this wrapping, and to facilitate external connection to the disc, the latter is preferably provided with a central raised portion l2, IS. The refractory insulating coating 6. 25 I preferably covers any wire wrapped around the central portion, thus not only insulating the surface of the disc, but helping to make a rigid joint to the electrode lead. In many cases, the connecting support between the electrode 4 (or 6) 30 and the disc 2 (or 3) should be covered with insulation, to prevent the discharge from occur ring to it.

What I claim is:

1. An electric gaseous discharge lamp of the as type having a filling of an inert gas and mercury vapor and comprising an elongated glass tube having sealed across each of its ends a metal closure disc with an inward peripherallygrooved protuberance of smaller diameter than 40 said disc, a wire wrapped around said protuberance and in said groove, an alkaline earth oxide coated electrode supported from said wire, and a refractory insulating coating over the interior surface of the disk and over the wrapped wire. 45 said coating bonding the disk and wire into conductive contact and insulating them from the gas filling inside the lamp.

2. An electric gaseous discharge lamp as in claim 1, in which the refractory insulating coat- 50 ing is of alumina.

JAMES L. COX. 

